Wet spring means delayed hatches

Mayfly hatches tick through a fairly typical schedule: Hendricksons, blue-winged olives and mahogonies start hatching in mid-April, marking the beginning of dry fly season. Usually, that beginning coincides with Michigan’s trout season opener — the last Saturday of April.

But after a hot two weeks in early March 2012, Hendricksons began popping off in March, well ahead of schedule.

This year should be a little more typical — even a touch later, said Ashley Moerke, biology professor at Lake Superior State University.

“So many of those hatches are temperature-controlled,” she said. “Given the colder temperatures to this point, we would expect them to be delayed a bit.”

Duke Elsner, small fruit educator with the Michigan State University Extension in Traverse City who holds a doctorate in entomology, says it won’t be the air temperatures that trigger their schedule.

“It’s the water temperatures that really rule them, and water temperatures don’t change as radically or quickly as air temperatures go,” he said.

Bugs in the nymph stage store warmth in their bodies, gaining what’s called a “degree day” each time temperature reaches a specific point. Once they hit the appropriate degree days, insects emerge. Each species of insect has a different temperature range that causes them to hatch.

“It’s really hard to guess the exact details about what makes them go for a flight,” Elsner said. “But we can’t really base too much on what we experience as weather temperatures. It’s a very different world underwater.”

While air temperatures have been cooler than normal, bugs have probably been experiencing normal conditions on the stream bed, Elsner said. Where air temperatures will affect bugs is after they’ve hatched and gotten above water.

During warm days, bugs tend to use up their reserves faster — especially mayflies, which don’t feed as adults, Elsner said. The bugs generally are more active and pass through their adult activities quicker, causing the hatches to last a shorter period of time.

So this wet, but more typical, spring set off mayfly hatches at a more typical rate.

Ethan Winchester, head guide at Boyne Outfitters at Boyne Mountain Resort, said fly anglers were reporting a few bugs popping off during opening day.

“It sounded like a good day, especially with the warm weather we were having,” Winchester said. “There were sporadic Hendricksons here and there, people getting fish on the surface.”

Winchester said anglers also reported seeing blue-winged olives.

Springs that are too hot and too dry tend to throw hatches off kilter, Winchester said.

“With a hot year, you have a lot of bugs come off real fast, and they’re done,” he said.

This year, those hatches should last several days — as they’re supposed to, he said.

“The hatches are later this year than last,” he said. “We’re still in runoff season — this is more of a normal Michigan spring than the past few years. The past few years have been too early, too hot, too dry.”

A very wet year has its own challenges, Moerke said. In the Upper Peninsula, rivers are still flowing hard and fast, carrying loads of sediment. That can impact bug habitat.

“The water is so turbulent right now,” Moerke said. “It’s like a sand-blasting effect on those insects.”

Even so, Moerke said the higher water levels and cooler temperatures are welcome over a hot, dry year like 2012. Most of the river systems in the eastern Upper Peninsula and northern Lower Peninsula are fed by groundwater, she said. The standing, “ponding” water will slowly sift into the ground, recharging aquifers and letting water into the system later in the season.

“It will be good to have the normal base flow,” she said. “We need some recharge groundwater in these regions to help sustain flows.”

Those pulses of snowmelt and rainwater later in the season don’t just benefit river levels. They carry nutrients into the river system in the form of nitrogen, phosphorous and carbon, Moerke said.

These nutrients aren’t runoff from farms or golf courses, she said. Rather, in the more remote, cold-water systems, these are naturally occurring nutrients from the breakdown of leaves and other formerly living things.

The significant snowmelt will help carry nutrients into water later in the season than normal, providing a buffet for cold-water insects, Moerke said. A healthy population of cold-water insects means a healthy buffet for trout.

Regardless of whether bugs — and trout — were a sure bet, Winchester said anglers speckled Northern Michigan streams in pursuit, and anglers reported seeing a few healthy hatches in the area.

“It was a good opening day,” Winchester said. “People were happy. It was sunny. It was good.”